Field of the Invention
In many instances, polypeptides are available which have one or more undesired amino acids or amino acid sequences. This situation has become of acute importance with the use of hybrid DNA technology to produce a wide variety of polypeptides of physilogical interest. In many situations, amino acid sequences are obtained which may include one or more peptides of physilogical interest or peptides having an undesired presequence or undesired initial amino acids. This can be a result of other requirements which require that the preparation of the polypeptide include the presence of the undesired amino acids or that convenience makes it desirable to produce a group of peptides on the same chain. In some situations, flanking DNA sequences may be expressed.
In these situations, it would be desirable to be above to remove the sequences or excise the desired peptide from the extended polypeptide. Therefore, ways have to be devised where polypeptides may be modified by removal of terminal amino acids or terminal sequences or by cleavage at predetermined sites to excise a peptide of the desired composition.